Q.What are the valence electrons? For s-block and p-block elements show that number of valence electrons is equal to its group number.

Step 1. Define valence electrons. The electrons present in an atom's outermost (valence) shell, which participate directly in chemical bonding (section 7.5.3).

Step 2. Show it for s-block. Group 1's general outer configuration is $ns^1$ → 1 valence electron, matching group number 1. Group 2's is $ns^2$ → 2 valence electrons, matching group number 2 (Table 7.1).

Step 3. Show it for p-block. Group 13's general outer configuration (from period 2 onward) is $ns^2np^1$ → 3 valence electrons; group 14 is $ns^2np^2$ → 4; group 15 is $ns^2np^3$ → 5; group 16 is $ns^2np^4$ → 6; group 17 is $ns^2np^5$ → 7; group 18 is $ns^2np^6$ → 8 (Table 7.6). In each case the valence-electron count is exactly (group number − 10): 13−10=3, 14−10=4, ..., 18−10=8. …

Deriving valence-electron count from each group's general outer configuration a …

• Forgetting the '−10' adjustment needed for p-block groups (13-18), and instead expecting valence electrons to equal the raw group number even for group 13 onward. …